1)A Brownish/Blackish and or Redish mark that is found in a towlet or human being's under shorts or panties. Found around the area of the anus.
2)A person that is a total fuck up and totally useless.
Like definitions may be found with Dumdass, Skidmark, Shit For Brains, Stupidass, Jerkoff, Spinout or Speed Racer.

I was taking a leak in Tommy's badroom, then I saw his Dad's boxers on the floor. There was bloody "shit stain" in them. It looked like he wiped up the floor with them after a blod bath.

its shit that got hammed into your underwear. occurs when u dont wipe your ass after a soupy shit, some gets stuck on your ass crack and this is called (magoo) this could harden into a poob(see poob), also, if somebody is trying to act funny by doing a fake fart, and that results in shitting in your pants and no funny farting sound, u have gained nothing funny out u it, but only a nasty shitstain on your underwear that is embaressing to yourself and others when they see it, or find out about it...

he took a crap, but all his ass hairs prevented it from reaching the toilet and acted as a net, he also ran out of toilet paper, so he went to the store and he came home and later found a shitstain that got hammed on his underwear